The present invention relates to a new and improved method of, and apparatus for, supporting a continuously cast strand, especially a steel strand, fabricated during a continuous casting method for strands, wherein the liquid core of the casting or strand is stirred by electromagnetic action.
It is known in the strand casting art to support and guide by means of support guide elements, for instance rolls, a steel strand emanating out of the continuous casting mold until there has been accomplished complete solidification of the strand. In most instances the strand is transferred from along an arcuate-shaped guide path into a horizontal path. Depending upon the size of the strand format or sectional shape which is to be cast there are required along such guide path different numbers of successive guide rolls, so as to prevent any bowing-out of the strand shell or skin due to the ferrostatic pressure of the liquid core.
Furthermore, it is known in the art to obtain by electromagnetic stirring of the melt in the liquid core of the strand an improvement in the quality of the cast product. The solidification structure should be affected in such a manner that there is produced as large as possible zone of compact or dense, equiaxed crystal structure with uniform distribution of the elements tending towards segregation over the strand cross-section. For physical reasons it is attempted to place the electromagnetic stirrer as closely as possible to the strand surface, so that there can be obtained a sufficiently great penetration depth of the traveling electromagnetic field with the smallest possible electrical losses.
Because of the required small spacing between successive guide rolls when casting large strand sectional shapes or formats and the thus small amount of available space, it is only possible to obtain the desired small spacing of the stirrer from the strand surface when resorting to structural aids which, in turn, are associated with appreciable drawbacks. With a state-of-the-art arrangement of the electromagnetic stirrer there is generated an induction stirring field for the molten core or pool of the casting at the direct neighbourhood of one longitudinal side of the cast slab. Directly above and below the stirrer there is accomplished supporting of the strand shell by smaller guide rolls connected with the stirrer, in order to maintain as small as possible the spacing between successive guide rolls at the region of the stirrer. However, this arrangement is afflicted with the drawback that for the build-up of an induction field which is effective at the slab there must be used a relatively large stirrer which has a not inappreciable width in the slab lengthwise direction. Consequently, the spacing between the guide rolls automatically becomes greater than the standard spacing. At the direct effective region of the stirrer it is however not possible to support the strand, so that there can arise undesired, damaging bowing-out of the strand skin or shell.
Furthermore, the liquid pool or core of the casting is only moved directly at the effective region of the stationary stirrer, so that due to the limited stirrer size there is also limited the quantity of the agitated or stirred steel.